Most of the process plants use steam for different heating applications, as it is one of the cheapest and effective media for heating applications. Once the steam is used in process heating application it gets converted to condensate. Often it is necessary to pump this condensate (from heating equipment located at different locations in the plant), back to the feed water tank in the boiler house. Making the most out of the Energy in steam system is the key to efficient operation. Yet, industries may be pouring useful of heat energy down through drains with the condensate that is being discharged from steam traps. It is not enough to simply remove the condensate from steam system; the true benefits come from adopting a simple condensate recovery.
Condensate Recovery
Condensate recovery enables to reclaim the condensate that is routinely discharged from steam traps by re-circulating it to boiler for use in producing additional steam. By doing this, one will find savings in a number of areas, such as:
Recapturing lost heat energy—instead of losing the usable Energy in the condensate, re-circulate them to the return to main and boiler feed water system for use in producing additional steam.
Lowering make-up costs—returning hot condensate not only conserves energy, it also lowers costs for preheating boiler make-up water.
Reducing operating costs—instead of sending treated water down the drain, a condensate recovery system will return it to the boiler where it will be re-used without requiring additional treatment chemicals.
Methods of Condensate Recovery:
1. Centrifugal Pump:
                Some plants use electric pumps for pumping the condensate. However, condensate is often hot at temperature greater than 100° C., which gives rise to Cavitation of the pump/impeller. (Centrifugal pumps generate lower pressure behind the impeller. The hot condensate temporarily evaporates and expands on the back side of the vanes). Over a period of time this will cause erosion and reduce the life of pump impeller.2. Pressure Powered Pump:        Pressure powered pump is a positive displacement pump operated by pressurized steam or pressurized air or pressurized gas for pumping the condensate back to the feed water tank. Pressure Powered Pumps (hereafter referred as PPP) are designed to move condensate without the use of electricity, and return condensate at high temperatures which is a limitation in case of typical conventional electric pumps (This limit is due to the fact, that above this temperature Cavitation occurs at the eye of impeller of centrifugal pumps, which damages impeller and pump body and badly affects pump operation). Since PPP are pressure-operated, they require no electrical panels, starters or accessories.        
Liquid dispensers powered by gas pressure, especially steam pressure, have a number of benefits for liquid dispensing system. Such liquid dispensers can operate under various conditions of pressure or vacuum and do not require seals or packing as do liquid dispensers powered by rotary machines or having pistons or centrifugal impellers.
Pressure driven liquid dispensers consume a minimal amount of power and generally provide a durable and cost effective solution to liquid pumping needs in various situations. A typical liquid dispenser driven by gas pressure comprises a tank having a liquid inlet and a liquid outlet near the bottom of the tank, with an inlet check valve and an outlet check valve permitting flow only in the liquid pumping direction. The tank also has a gas inlet and a gas exhaust outlet located higher on the tank, above the maximum liquid level. The gas inlet and gas outlet have valves that are operated reciprocally, such that the gas or pressure inlet is open when the gas outlet or exhaust is closed, and vice versa, as a function of the level of liquid in the liquid dispenser tank.
For example, the gas inlet valve and gas outlet valve can be coupled to a float mechanism. Alternatively, the liquid level in the tank can be sensed by electrical level sensors that produce a signal for triggering the gas or pressure inlet/outlet valves to reverse positions. The operation requires a certain hysteresis, with the gas inlet opening and exhaust closing when the fluid level reaches a high threshold level, and remaining in that position until reversing when the fluid level drops below a low threshold. The difference between the thresholds, which can be sensed in a variety of ways, defines the stroke of the liquid dispenser.
One arrangement in which the liquid level is sensed using a float and the valves are operated mechanically, involves a snap action linkage that simultaneously opens the gas inlet and closes the gas outlet, or closes the gas inlet and opens the gas outlet, at the two thresholds. Examples of such snap action float mechanisms and liquid dispensers are disclosed in U.S. Pat. No. 5,230,361-Carr et al.; U.S. Pat. No. 5,366,349—fig; U.S. Pat. No. 5,141,405—Francart, Jr.; and U.S. Pat. No. 1,699,464—Dutcher.
In other arrangement a pressure powered pump wherein float being operatively connected to a spring-loaded over-center mechanism includes valve actuating means acting on the valve elements which is movable between defined positions, by stop means for arresting movement of the valve actuating means in the stable positions as in European patent GB 2302916; a float operated device for a pressure powered pump where float operates a toggle mechanism composed of an input lever carrying a float, and an output lever, the levers pivotably mounted at spaced locations on a common support, a resilient means act between said levers and said resilient means acts to bias the output lever into the other of its limit positions as in U.S. Pat. No. 6,174,138 and a pump with spring assisted float mechanism, an over-center snap-action mechanism mechanically linked to the ball check valve assembly as in U.S. Pat. No. 6,602,056.
The liquid dispenser has a cycle including a liquid filling phase, pressurizing/pumping phase and a depressurizing phase. During the liquid filling phase the gas inlet is closed, the gas outlet is open, and the liquid, which can be water or some other liquid, flows at a relatively low pressure through the liquid inlet check valve to fill the tank. This filling flow can be powered by gravity or another form of low pressure flow. The liquid outlet check valve remains closed because the pressure of the liquid in the tank is relatively low. Tank pressure is low because the gas exhaust valve is open, and the flow line downstream of the outlet check valve may be pressurized as well, either of which keeps the outlet check valve closed. The exhaust valve may vent into the atmosphere, or it may vent into a closed conduit or vessel at a pressure less than the liquid inlet head.
As the float rises in the tank with the level of liquid, the float mechanism reaches a crossover point and toggles the gas valves to open the gas inlet and close the gas outlet, switching from the liquid filling phase of the cycle to the liquid discharge phase. Gas under pressure, such as steam, pressurizes the tank through the gas inlet valve, the gas outlet valve now being closed. Gas pressure builds in the tank; reverse biases the liquid inlet check valve, and forward biases the liquid outlet check valve. The liquid in the tank is forced by gas pressure through the liquid outlet check valve and downstream of the liquid dispenser, at the pressure of the steam or other gas. When the float drops past a low crossover point, the gas inlet valve closes and the gas outlet valve opens, venting the pressure in the tank and permitting the cycle to repeat.
In this manner the tank alternately fills with low pressure liquid and discharges at higher pressure through the liquid outlet. The liquid dispenser is useful for returning or inserting liquid such as water into a pressurized system using the pressure in the system as the motive pressure force. This is particularly useful in connection with steam power and heat exchange systems. However, all that is needed is a pressure differential. Thus, the liquid dispenser is useful in closed loop arrangement in which one or more of the inlet liquid feed to the tank, the gas exhaust from the tank and the outlet, are at elevated pressure as compared to-ambient.
Although a pressure liquid dispenser as described is durable and useful, there are certain limitations inherent in its structure, resulting in limitations on the flow or liquid dispensing capacity of the liquid dispenser. In as much as liquid filling typically is accomplished at low differential pressure (e.g., by gravity) through isolation valve, strainer and non-return valve, the liquid fill rates are too slow. During pumping phase, pressurized media at sufficient pressure and flow is must, as it initially spread in pressure chamber and then starts the pressurizing of the liquid in pressure chamber, this increases pumping phase time. This time depends on flow rate, port size of pressurizing port and pressure and flow rate of the pressurizing media. When switching from the pressurized pumping phase to the vented exhaust stage, time is required to permit the gas pressure in the tank to vent before low pressure liquid can begin to fill the tank through the liquid inlet check valve. The time taken to reduce the internal tank pressure to a lower pressure than the inlet line depends on several factors including the extent to which the tank was pressurized and the internal diameter and back pressure of the gas exhaust valve and conduit. The need to vent and reduce tank pressure to shift from positive to negative pressure differentials between the tank and the liquid inlet (to open the inlet check valve and allow an in-flow) and between the tank and the liquid outlet (to close the outlet check valve), respectively, provide an inherent cycling delay and a corresponding limitation on the flow rate of the liquid dispenser.
It is known that a very large pressure inlet and exhaust orifice is provided in order to pressurize and depressurize the pressure chamber to reduce overall cycle time. However, these attempts were not too successful due to seating problems of large orifices at higher pressure, also these valves must be forced open against the pressure in the tank at the point of the switchover between cycles, for example by the force generated by the spring of a snap over float mechanism.
Where the gas inlet and outlet valves are linked mechanically, the device that opens the gas inlet valve and closes the gas outlet valve is opposed by differential pressure between the pressure source and the tank for opening the inlet to commence a pumping phase, and between the tank and the vent for opening the outlet valve to commence filling phase. In a liquid dispenser vented to the atmosphere the pressure differential in each case is substantially equal to the difference between the gas supply pressure and ambient pressure or in a closed system the differential is between the pressures of the gas supply and the vent line.
If one chooses to enlarge the orifice size of the exhaust valve to speed or improve venting, the flow area of the exhaust valve body is increased. As a result, a correspondingly larger force is needed to open the exhaust valve against the pressure differential, because the same force per unit of area is applied to a larger area. It is not desirable to add heavier springs or other expensive mechanical features to the mechanism like bigger float. Larger float arm operates the respective valves. Likewise, larger valves are generally more expensive and technically demanding than smaller ones, particularly for high pressure applications.
What is needed is a means to reduce the flow restriction at the inlet and exhaust of a liquid dispenser that is to enlarge the exhaust orifice, without the drawbacks of a large valve including the need to obtain added mechanical opening force in the valve operating mechanism. Further, the valves structure should deal with the problem of pumping and venting steam such that the steam does not substantially slow down the venting of pressure or the inflow of water.